This invention relates to transmission columns and in particular motor vehicle steering columns which separate on impact.
When a motor vehicle is subjected to a frontal impact, the steering wheel carried by the steering column is liable to be displaced towards the driver in the passenger space of the vehicle. One of the solutions retained to avoid this displacement of the steering wheel, endangering the driver, consists in rendering the steering column separable on impact. To achieve this, two sections of a steering column are connected by two plates each fitted to a section and joined together by two pins which are rigidly locked to one of the plates, and mounted so as to slide axially in orifices provided in the other plate. This type of construction was the object in particular of French patent 85.07.792 filed by the Applicant.
However, under certain operating conditions, this type of separable coupling has the drawback of separating without there being any real impact.
The object of this invention is to propose a safety assembly for a separable coupling device which guarantees that this link will remain intact in all conditions of use of the vehicle except in the case of a frontal impact whose predetermined threshold value is such that the separable coupling device actuates.
In accordance with the invention, the safety assembly for a separable coupling device, particularly for a motor vehicle steering column, includes two coaxially arranged shaft sections whose end portions are offset with respect to their common geometric axis and which overlap, said end portions each carrying a plate. Each of these plates is connected to the other plate by separable link pins. The safety assembly comprises a clip made up of a fork having two faces connected to each other by a web so that each of the two faces bears against one side of the corresponding plate:
one of the two faces has a system for attaching one of the ends of one part of the link pins; PA1 the other face has a system for clamping one of the ends of the other part of the link pins; PA1 one of the two faces is provided with openings intended to receive the corresponding end of the link pins that are not connected to the face, in such a way that the said clip blocks the axial separation of the two plates with respect to each other when this separation occurs at slow speed, while at the same time permitting this separation when it occurs at high speed. PA1 the said link pins fixed to each plate are engaged in holes provided in the other plate via bushings; PA1 one of the two faces of the clip has a system for attaching the bushings of one part of the link pins; PA1 the other face of the clip has a system for clamping the bushings of the other part of the link pins; PA1 one of the faces is provided with openings intended to receive the corresponding end of the link pins whose bushings are not connected to said face. PA1 each plate is provided with an orifice in which the end portion of the corresponding shaft section is engaged; PA1 each plate comprises two lateral protrusions which delimit between them a hollowing for the passage of the end portion to which the other plate is fixed; PA1 the link pins are each fixed in a lateral protrusion of each plate. PA1 is made up of a fork having two faces connected to each other by a web; PA1 one of the two faces having an attachment system made up of two holes receiving the bushes of the link pins; PA1 the other face having a clamping system made up of two openings provided with a narrowing which receives the bushings of the other link pins; PA1 one of the faces also has two holes intended to receive the corresponding end of the link pins whose bushings are not connected to said face.
More precisely, the safety assembly, in accordance with the invention, is characterized in that:
To the advantage of the separable coupling device in accordance with the invention:
To ensure even greater reliability of the system, the safety assembly in accordance with the invention comprises a fusible plate arranged between the two plates and between each of the plates and the end portion carrying the other plate, this fusible plate being secured at each of its two ends to the side of the corresponding plate in such a way that the said fusible plate blocks the axial separation of the two plates with respect to each other when this separation occurs at slow speed and for a lower value than that of the clip, while permitting this separation when it occurs at high speed.
In accordance with a particularly interesting embodiment of the invention, the clip:
In order to ensure best possible adaption to the structure of the separable coupling device, the fusible plate is made up of a central part provided with a neck and two ends. The width of the central part is chosen according to the width of the hollowings of the plates. One of the ends is shaped as a heel in order to bear against the face of the corresponding plate, whereas the width of the other end is substantially equal to the width of the central part and has two wings which are folded back, at the end of assembly, against the face of the other plate.
Thus the safety assembly in accordance with the invention presents the advantage of being able to be installed in a separable coupling system for a steering column, the object of which is to make it possible for the steering shaft of a motor vehicle to separate in the event of a frontal impact so as to prevent the steering wheel from rising towards the driver. This safety assembly in accordance with the invention makes it possible to add a safety device comprising a clip and a fusible plate which act separately from each other. The other features of this assembly, which are particularly advantageous, are that it does not modify the separation forces of the separable coupling device, and intervenes only for forces whose value is clearly different from that of the impact threshold at which the separable coupling device intervenes. Moreover, the clip blocks the axial drift of the two plates when it occurs at slow speed by means of holes made for this purpose on one of the faces of the clip, the clip then interfering with the corresponding end of the link pins. In contrast, when it occurs at high speed, the clip does not block this axial separation of the two plates with respect to each other, i.e. in dynamic mode, which is the case in impacts for which the separable coupling device was initially designed, since the ends of the link pins do not have time to engage in the holes made in the corresponding face of the clip.